"My another question is about the reason of using the ++. If the 0(false) is added to 1, what's the incrementing for? It's not like an iterator's or a pointer's moving we normally see. The increasing didn't change anything seemingly."

I don't understand what point you're making here. Take a look at these two scripts: the first with ++, the second without. 

$ perl -Mstrict -Mwarnings -le '
    my @fields = qw{a a b c b a};

    my %seen;

    for my $field (@fields) {
        print $field, $seen{$field}++ ? "PUSH" : "SET";
    }
'
aSET
aPUSH
bSET
cSET
bPUSH
aPUSH

[download]
$ perl -Mstrict -Mwarnings -le '
    my @fields = qw{a a b c b a};

    my %seen;

    for my $field (@fields) {
        print $field, $seen{$field} ? "PUSH" : "SET";
    }
'
aSET
aSET
bSET
cSET
bSET
aSET

[download]

That may clarify whatever is causing confusion or misunderstanding. If not, please supply a similarly short piece of code to explain your point.

"... I decided to find some artical about Perl Ops priority to read first."

Take a look at "perlop - Perl operators and precedence". There's a table of precedence and associativity at the start of the documentation. While you're there, you might as well also look at these sections further down the page: "Auto-increment and Auto-decrement" for "++" and Conditional Operator for "?:".

-- Ken

In reply to Re^3: What's this line means in HTTP::headers? by kcott
in thread What's this line means in HTTP::headers? by anaconda_wly

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